Dairy proteins like the caseins and whey proteins are among the most widely used food ingredients. Also other proteins like soy protein and chicken egg protein are commonly used food ingredients. A property of many of these proteins is that they are surface active, some more than other, which means that many of these proteins can act as emulsifiers or foam stabilisers in food products. In many cases however it is undesirable that the proteins are surface active, as it may lead to foaming or emulsification problems in manufacturing processes. Nevertheless due to its nutritional properties and for example texturising properties, food formulators still want to include the proteins in their food products. Hence there is a desire to use proteins which have strongly reduced surface activity.
It is well known that dairy whey protein can be formed into particles, by heating whey protein under shear. For example, WO 91/17665 disclose a process for the formation of microparticulated denatured proteins, wherein the microparticulates are water-dispersible. WO 93/07761 discloses spray dried microparticulated protein product characterized as an agglomerate of rehydratable proteinaceous microparticles surrounded by a soluble matrix. WO 2006/058538 discloses a method for preparation of denatured whey protein microparticulates. U.S. Pat. No. 4,734,287 discloses a macrocolloid containing non-aggregated particles of whey protein.
It is also known that heat treatment reduces the ability of whey protein to act as foam stabiliser. Phillips et al. (Journal of Food Science, 1990, vol. 55, p. 1116-1119) disclose that the heat treatment of whey protein solutions reduces the foaming ability of these solutions. Dissanayake et al. (Journal of Dairy Science, 2009, vol. 92, p. 1387-1397) disclose a method to produce whey protein particles, which do not show foaming ability. The process involves a heating step at 90° C. for 20 minutes, subsequently a high pressure microfluidisation step at 140 MPa is performed, and this is followed by spray drying the obtained material.
Nicorescu et al. (Food Research International, 2008, vol. 41, p. 707-713) disclose that heating of solutions of whey protein influences the surface tension of these solutions: heating leads to a surface tension of about 40 to 50 mN·m−1, which means that the proteins are less surface active as compared to non-heated proteins. The thermodynamic affinity of protein aggregates towards air interfaces is weaker, however the proteins as disclosed are still surface active.
In a continuation of this work, Nicorescu et al. (Food Research International, 2008, vol. 41, p. 980-988) disclose that insoluble aggregates of whey protein apparently have the role of foam depressors.
EP 1 839 492 A1 discloses a method to prepare whey protein micelles by heating an aqueous whey protein solution at a pH between 3 and 8 to a temperature between 80 and 98° C., in the absence of shearing, followed by a concentration step. The last step is required to remove non-micellised material, or simply for concentration. The obtained micelles have a very small average particle size, and this material can be used as an emulsifier or as a foam stabiliser. This means that the micelles are still surface active.
EP 485 663 Al discloses a method wherein whey protein is partly denatured, and subsequently at least part of the undenatured protein still present is removed. This material can act as emulsifier.
WO 2007/136263 A1 discloses a method to produce protein particles, and use these particles as encapsulation material, wherein the particles are produced by heating a protein. No separation step occurs wherein surface active material is separated from non-surface active material, hence the particles obtained will still be surface active.
U.S. Pat. No. 6,767,575 B1 discloses an icecream containing protein aggregates. The aggregates are prepared by heating whey protein such that at most 90 to 95% of the whey is denatured. This means that the whey protein particles will still be surface active.
WO 2007/071405 A1 discloses hydrophobic denatured protein particles, which still are surface active, as they may be located at the oil-water interface of an emulsion.
EP 1 889 544 A1 discloses interfacially active particles which may be made out of protein aggregates.
U.S. Pat. No. 4,855,156 discloses a frozen whipped dessert comprising non-aggregated particles of denatured protein. These particles are still surface active.
A common disadvantage of all protein particles and aggregates as cited, is that they are still surface active. Hence when preparing an aerated or foamed composition containing proteins, e.g. an aerated or foamed food product containing proteins, these protein particles will be present at the gas bubble interface. The surface activity of such particles may be relatively low, however as proteins are generally present at relatively high concentrations in compositions like food products, the number of particles at the gas bubble surface will be relatively high. Hence such particles may interfere with stabilisers present at the gas bubble interface, and compete for space with such stabilisers at that interface. As the number of protein particles is generally high, the protein particles will win such competition, and as they are not very strong gas bubble stabilisers, this will lead to instability of the gas bubbles and collapse of the aerated structure of the composition.